In recent years, efforts have been devoted to improve the luminance of the LED in order to apply the device to the lighting domain, and further achieve the goal of energy conservation and carbon reduction. The enhancement of the luminance relies on improvement of internal quantum efficiency (IQE) by improving the quality of epitaxy layers to increase the recombination rate of electrons and holes. Another way is to improve the light extraction efficiency (LEE) by effectively guiding light emitted by light-emitting layer out of the device and lowering the amount of light internally absorbed by the structure of the light-emitting device.
Surface roughness technology serves as one of the effective ways to improve luminance. A well-known method of surface roughing is mechanically polishing the surface of the substrate to form randomly distributed rough surface which is difficult for controlling the roughness such as depth or width effectively so reproducibility is worse. Besides, it is hard to control quality of epitaxy layers and more likely to cause epitaxy layers of poor quality forming epitaxy layers on the un-uniform surface when applying the method on mass production.